Permeability tuned band-spread circuit



June 18, 1946. J. J BRAND 2,402,261

PERMEABILgI"! TUNED BAND S PREAD C IRCUIT Filed Nov. 21, 1942 CHANGE Kc OSCILLATOR Fe: .=/014k\ INVENTOR JEAN JA wuss BRA/VD.

MOT/0N or Cone Kg =(X) (Emm'ns oF4/v llvcu) ATTORNEY Patented June 18, 1946 PERMEABILITY TUNED BAND-SPREAD CIRCUIT Jean Jacques Brand, Arlington, Va., assignor to Radio Corporation of America, a corporation of Delaware Application November 21, 1942, Serial No. 466,417

The present invention relates generally to short-wave permeability tuned circuits, and

more-particularly to auxiliary means for use in conjunction with such circuits for effecting bandspread tuning thereof.

There are a number of methods known in the art for obtaining band-spread tuning in the short-wave bands, as for example, shuntin a separate coil across the main tuning coil to tune to each band, or the use of a variable capacitor across the whole or a portion of the coil. Ac-

cording to the. present invention separate coils and capacitors are not employed but instead there is provided an auxiliary powdered iron core, movable independently of the main tuning core for band-spreading desired portions of the shortwave bands.

It is therefore one of the objects of the invention to provide a simple means for obtaining band-spread tuning in a permeability tuned circuit.

Another object of the invention is to provide an adjustable powdered iron core in conjunction with the main tuning inductance of a permeability tuned circuit for effecting band-spread tuning of the circuit.

A still further object of the invention is to effect band-spread tuning in a superheterodyne receiver by associating an independently adjustable powdered iron core with the main oscillator inductance whose flux is constrained by a shield can.

The invention will be further understood from the following description, when considered in connection with the accompanying drawing and its scope is pointed out in the appended claims.

In the drawing,

Fig. 1 illustrates a conventional permeability tuned circuit to which the present invention has been applied.

Fig. 2 is a view in cross-section showing the structure of the elements constituting the permeability tuned circuit shown in Fig. 1,

Fig. 3 shows a curve depicting the frequency change in the circuit with adjustment of the auxiliary core, and

Fig. 4 shows the application of the invention to a superheterodyne receiver.

Referring to Fig. 1, the circuit I comprises a main inductance coil L1 and a shunt capacity C which constitute the well-known permeability tuned circuit. A movable powdered iron core K1 is adapted to cooperate with the coil L1 in a known manner to vary its inductance and thereby to change the tuning of the circuit. The tun- 3 Claims. (01. 25040) able circuit I is shown connected to a tube 2 which may be either a radio frequency amplifier or a detector-oscillator.

According to the invention there is provided an auxiliary powdered iron core K2 having good permeability and Q factor, which is suitably spaced from and adapted to be moved in parallel relation to the inductance coil L1 of the permeability tuned circuit. A suitable structural arrangement of the coil L1 and the main and auxiliary cores K1 and K2 is illustrated in Fig. 2. Suitable insulating coil forms 3 and 4, arranged in parallel and spaced apart substantially center to center, are centered within the shield can 5. The coil L1 is wound on the coil form 4, and for the particular circuit shown I have used a 26 turn, #25 En. wire, wound to a length of 1% inches, with the main tuning core K1 of Carbonyl grade E iron. The auxiliary iron core K2, which may be of similar material as the core K1 although not necessarily so, is mounted for sliding motion within the other form 3. The shield can 5 serves to constrain the lines of. flux about the inductance coil L1.

The effect of operating the auxiliary core K2 close to the coil L1 will be seen from the curve shown in Fig. 3. The circuit was adjusted to resonate at an arbitrary frequency of 10 me. .by appropriate adjustment of the main core K1. Then the auxiliary core K2 was moved in steps of A" from a position where the entering end of the core was in line With the end of coil L1 to a fully entered position. It will be observed from the curve so obtained that a frequency change from to 160, or a total change of about 250 kc., takes place and that it is substantially linear for a considerable portion of the core travel. In the use of the invention, for effecting band-spread tuning in one of the short-wave bands, the auxiliary core K2 is first moved to a position corresponding to the center of the most linear portion of the curve shown in Fig. 3 which in the example given is the position attained by the core with a travel of about of an inch. With the coil K2 50 positioned the main core K1 is then adjusted to tune the circuit to the centerfrequency of the band which it is desired to spread. The auxiliary core K2 is then moved in one direction or the other from its original setting for eifecting the band spreading. It was found necessary with the arrangement disclosed to use the shield can so that the lines of flux about the main coil would be constrained. Measurements made using no shield gave very small amounts of frequency variation even for very close spacing between the auxiliary core and the circuit inductance coil.

The band-spreading means above described may be utilized in signal frequency circuits as Well as in the oscillator circuit of a superheterodyne receiver, or in both. In Fig. 4 I have shown the invention applied to a superheterodyne shortwave receiver. The signal frequency circuits l associated respectively with the antenna A and with the radio frequency amplifier tube 6 are similar to the permeability tuned circuit l of Fig. 1. The tunable circuit 7 associated with the detector-oscillator tube 8 is provided with a coil L2 having a smaller number of turns per inch in order to track said circuit with the circuits I, as described and claimed in the co-pending application of W. F. Sands, Ser. No. 463,192, assigned to the same assignee as this application. The main tuning cores K1 are mechanically connected for uni-control operation as shown, and are settable selectively by suitable means, not shown, to a center-frequency position of any one of a plurality of short-wave bands. The respective auxiliary cores K2 associated with the antenna, signal frequency and oscillator circuits are also mechanically united, as shown. to adapt them for uni-control operation and for efiecting bandspread tuning within the selected short-wave band, as explained above.

While I have shown and described a preferred embodiment of the invention, it will be understood that modifications and changes may be made without departing from the spirit and scope of the invention, as will be understood by those skilled in the art.

What I claim is:

1. A variable permeability-tuned circuit comprising a coil of the solenoid type, a main magnetic core movable axially within the coil for varying its inductance, and, therefore, the tuning of the circuit over a plurality of space-apart bands in the short-wave portion of the radio frequency spectrum, an auxiliary magnetic core dis- 4 posed close to said coil and movable axially in a direction substantially parallel to that of the main core and adjustable in a continuous manner for effecting band-spread tuning of the circuit in each of said short-wave bands as determined by a particular fixed setting of the main core, and a shield can enclosing the coil and cores to constrain the lines of flux about the coil.

2. A variable permeability-tuned circuit comprising an inductance coil, a main magnetic core axially disposed within said coil, means for adjusting the axial position of the core to vary the coil inductance and, therefore, the tuning of said circuit over a plurality of spaced-apart bands in the short-wave portion of the radio frequency spectrum, an auxiliary magnetic core positioned externally of and close to the coil and with its axis in spaced, substantially parallel relation with the axis of the main core, means for adjusting the axial position of said auxiliary core in either direction from a neutral position to efiectba'ndspread tuning of the circuit in each of saidshortwave bands as determined by a particular fixed adjustment. of the main core, and a shield can enclosing the coil and cores to constrain the lines of flux about the coil.

3. A variable permeability-tuned circuit capable of being tuned through a plurality'of spacedapart bands in the short-wave portion of the radio frequency spectrum, comprising an inductance coil, a shield can enclosing the coil. a magnetic core movable within said coil to predetermined positions such that for each said position the circuit is tuned to the center-frequency of a corresponding short-wave band, and means for effecting band-spread tuning in each of said bands comprising a continuously adjustable magnetic core disposed within the shield can and close to the inductance coil and effective upon movement through its range to provide substantially linear frequency variation of said circuit Within each band above and below the center-frequency JEAN J. BRAND. 

